Heart failure refers to a clinical syndrome in which cardiac function causes a below normal cardiac output that can fall below a level adequate to meet the metabolic demand of peripheral tissues. Heart failure may present itself as congestive heart failure (CHF) due to the accompanying venous and pulmonary congestion. Heart failure can be due to a variety of etiologies such as ischemic heart disease. Cardiac decompensation is typically marked by dyspnea (difficulty breathing), venous engorgement and edema, and each decompensation event can cause further long term deterioration of the heart function.
Heart failure patients have reduced autonomic balance, which is associated with left ventricular dysfunction and increased mortality. Modulation of the sympathetic and parasympathetic nervous systems has potential clinical benefit in preventing remodeling and death in heart failure and post-MI (myocardial infarction) patients.
Clinicians set measured parameter thresholds in some known implantable medical devices, such as pacemakers, defibrillators, cardiac resynchronization devices, and the like. The threshold for each parameter may vary from patient to patient. Appropriate device therapy is triggered when a threshold is crossed. Treatment can be initiated by non-events that include measurements above at least some thresholds. These non-events are also referred to as false positives. Therapy delivered for false positives depletes battery power and may increase the risk of overstimulating the patient.
Improved methods and systems are needed to accurately determine heart failure status, and to provide heart failure therapy using the accurately-determined heart failure status.